1. School of Sciences, Lautoka Campus BIO509 Lecture 27: Respiration

2. Aerobic respiration is the biological process by which reduced organic compounds are metabolized and subsequently oxidized in a controlled manner.
Aerobic respiration is common to all organisms.
Respiratory process in plants is similar to animals and lower eukaryotes.

3. glucose & oxygen carbon dioxide & ATP
The equation for cellular respiration is the opposite of the equation for photosynthesis.
Reactants Products
glucose & oxygen carbon dioxide & ATP
A redox reaction where glucose is oxidized to CO2 while O2 acts as the ultimate electron acceptor.

4. Loss of hydrogen atoms (oxidation) Gain of hydrogen atoms (reduction)
C6H12O6
6 O2
6 CO2
6 H2O
Loss of hydrogen atoms (oxidation)
Gain of hydrogen atoms (reduction)
Energy
(ATP)
Glucose +

5. Photosynthesis provides the fuel for cellular respiration
CO2
H2O
Glucose O2
ATP
ECOSYSTEM
Sunlight energy
Photosynthesis in chloroplasts
Cellular respiration in mitochondria
(for cellular work)
Heat energy +
Photosynthetic organisms use light energy to:
Produce glucose + O2 from CO2 + H2O.
Cellular respiration produces chemical energy (ATP) by:
Breaking down glucose & consuming O2, producing CO2 + H2O.

6. Mitochondria are the sites of respiration

7. Respiration is divided into three stages.
1. Glycolysis (occurs in cytosol). 2. Citric Acid Cycle or Tricarboxylic Acid Cycle or the Kreb’s Cycle (occurs in the mitochondrial matrix). 3. Electron Transport Chain (occurs in the inner mitochondrial membrane).

9. Glycolysis Glycolysis occurs in the cytosol.
It does not require oxygen.
Produces only about 25% of the total energy from glucose.
Glucose (6-C) is first broken down to two 3-carbon sugars using ATP.
These are oxidized and rearranged to produce two molecules of pyruvate.
A small amount of energy in the form of ATP and NADPH is released from glycolysis.

10. Glycolysis 2
Produces 4 ATP molecules by substrate-level phosphorylation.
When an enzyme transfers phosphate from a substrate molecule directly to ADP to form ATP.

11. Reduces 2 NAD+ to form 2 NADH.
NADH molecules will be used to produce ATP in the 3rd stage of respiration (oxidative phosphorylation).
Since 2 ATP were used in the preparatory phase of glycolysis, there is a net gain of 2 ATP molecules for each glucose molecule that enters glycolysis.

12. Substrate-level phosphorylation
Enzyme transfers a phosphate group from a substrate molecule directly to ADP to form ATP.
This produces 4 ATP molecules in glycolysis.
Enzyme
Adenosine
Organic molecule (substrate)
ADP
ATP P
ATP

13. For each glucose molecule processed, what are the net molecular products from glycolysis?

14. Citric Acid Cycle (Kreb’s Cycle)
Occurs in the matrix of the mitochondria.
It has been found that in the absence of air, cells produced ethanol and lactic acid while in the presence of air they produced CO2 and H20.
The Kreb cycle was
discovered by
Hans Kreb in 1937.

15. For the Kreb cycle to function pyruvate generated in the cytosol during glycolysis needs to be transported to the mitochondria.
Between glycolysis & the citric acid cycle: pyruvate is converted to acetyl Coenzyme A (CoA consist of vitamin pantothenic acid and a nucleotide).

16. A carbon atom is removed from pyruvate & released as CO2.
The 2 carbon compound is oxidized while a molecule of NAD+ is reduced to NADH.
CoA joins with the 2 carbon molecule to form acetyl coenzyme A (acetyl CoA) which then enters the Kreb cycle.

17. Kreb’s Cycle Takes place in the matrix of the mitochondria.
Acetyl group (2 carbon) enters the cycle by combining with oxaloacetate (4 carbon), to form citrate (6 carbon). This initiates citric acid cycle.

18. As acetyl group passes round the cycle, the 2 carbon atoms are lost in CO2 in two decarboxylation reactions.
Hydrogen is added to hydrogen carriers in four dehydrogenation reactions, resulting in a total of 3 NADH2 and 1 FADH2 molecules.

19. Details of the citric acid cycle
2 carbons enter cycle in the form
of Acetyl CoA
CoA is stripped from AcetylCoA
and recycled.
2C + 4C forms a 6C compound (citric acid). 1
Step
NAD- Nicotinamide adenine dinucleotide
FAD - Flavin adenine dinucleotide
CoA – Coenzyme A
Succinate
FAD
FADH2
Malate
NAD+
Oxaloacetate
Citrate
leaves cycle
+ H+
NADH
Alpha-ketoglutarate
CO2
ADP + P
Acetyl CoA
CITRIC ACID CYCLE 2
CoA 1 3 4 5
ATP
Steps & 4 5
original 4C molecule is
regenerated by oxidation
to start cycle over again.
this produces 1 NADH
and 1 FADH2.
Steps & 2 3
2 carbons are completely oxidized to
CO2, producing 2 molecules of NADH.
1 ATP is produced by substrate-level
phosphorylation.

20. The main functions of the TCA cycle
Production of energy rich NADH, and CO2
Regeneration of oxalocatate. Producing NADH, FADH2, ATP

21. Glycolysis produces: 2 ATP
So far, Overall
Glycolysis produces: 2 ATP
Krebs Cycle produces: 2 ATP, 10 NADH and 2 FADH2

22. Electron transport chain and ATP synthesis in the mitochondria
Since cells only use energy in the form of ATP, the high-energy electrons present in the from of NADH and FADH2 need to be converted to ATP.
This occurs in the inner membrane of the mitochondria and requires oxygen via the electron transport chain.
The ETC consists of 4 large multi molecular complexes and two mobile carriers on the inner mitochondrial membrane.

23. Mobile carriers - ubiquione (Q) and cytochrome c (cyt c)

24. Electrons from NADH enters ETC at complex I (NADH –ubiquione oxidoreductase).
From here the electron moves to ubiquione. It is mobile and transports the electrons to from complex I to complex II.

25. Complex III acts as an oxidoreductase and oxidizes reduced ubiquinone, transferring the electrons to cytochrome c.
Cytochrome c is not an integral membrane protein in ETC and serves as a mobile carrier to electron transfer between complex III to complex IV.
Complex IV reduces O2 (using 4 electrons ) to water.

26. During the movement of electrons in the ETC H+ are moved from the matrix to the intermembrane space through chemiosmosis.
This creates a proton gradient.
Electrons move down the gradient through the ATP synthase complex.
It uses this energy to combine ADP and Pi to form ATP

27. Overall Aerobic respiration yields about 23-36 molecules of ATP per molecule of glucose.
NADH
FADH2
Cytoplasm
Electron shuttle across membrane
Mitochondrion
GLYCOLYSIS
Glucose
Pyruvate
by substrate-level phosphorylation
by oxidative phosphorylation
2 Acetyl CoA
CITRIC
ACID CYCLE
+ 2 ATP
+ about 34 ATP
About 38 ATP 2 6
(or 2 FADH2)
OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis)
Maximum per glucose:
~38
ATP
34+4=38

28. Questions??